eMedicine Specialties > Orthopedic Surgery > Neoplasms

Chondroblastoma: Differential Diagnoses & Workup

Author: Hannah D Morgan, MD, Consulting Staff, Connecticut Orthopaedic Specialists
Coauthor(s): Timothy A Damron, MD, David G Murray Endowed Professor, Department of Orthopedic Surgery, Professor, Orthopedic Oncology and Adult Reconstruction, Vice Chair, Department of Orthopedics, State University of New York Upstate Medical University at Syracuse
Contributor Information and Disclosures

Updated: Jul 18, 2007

Differential Diagnoses

Chondromyxoid Fibroma
Chondrosarcoma
Giant Cell Tumor

Other Problems to Be Considered

Chondromyxoid fibromas, which are found in patients in the same age group in which chondroblastomas are found, may mimic the latter radiographically and microscopically. Both types of lesions tend to have well-circumscribed lytic areas on radiographs, microscopically seen areas of immature cartilage and giant cells, and perilesional marrow edema on magnetic resonance imaging (MRI) examination. However, chondromyxoid fibromas most often arise from the metaphysis or metadiaphysis rather than from the epiphysis (where 90% of chondroblastomas are located), are devoid of calcification, and have a characteristic myxoid, pseudolobular pattern of organization, as well as more pleomorphic stellate cells.

Giant cell tumors of bone also may mimic chondroblastoma, as the epiphyseal location and histologic characteristics can be quite similar. However, the former are almost exclusively seen in patients who are skeletally mature, while chondroblastoma tends to arise in skeletally immature patients. Furthermore, the epicenter of a giant cell tumor lies within the metaphysis. On histologic examination, giant cell tumors have elongated cells that are clustered together, in contrast to the round or polygonal cells of chondroblastoma.

Calcifications and chondroid matrix also are absent in giant cell tumors. Eosinophilic granuloma is a lesion found in young patients that may appear in rare instances as a radiolucent epiphyseal lesion similar to chondroblastoma. However, microscopic examination reveals a more heterogeneous collection of cells, including histiocytes, granulocytes, and eosinophils. Finally, clear cell chondrosarcoma may have features that overlap those of chondroblastoma, but the presence of large cells with abundant clear cytoplasm and vesicular nuclei, as well as type II collagen and malignant chondrocytes, should distinguish this tumor. Typically, clear cell chondrosarcoma is an epiphyseal tumor of adulthood.

Workup

Laboratory Studies

• Laboratory studies are not routinely useful in the workup of patients with chondroblastoma.

Imaging Studies

• Adequate regional radiographs should be obtained in patients with suspected chondroblastoma (see Images 1-2).
• A bone scan may be helpful in assessing a lesion's biological activity; it can also aid in locating other regions of disease involvement that may result from entities other than a chondroblastoma or from the rare occurrence of multifocal chondroblastomas (see Image 3).
• MRI should be conducted if any question exists about the diagnosis or lesion boundaries, including perilesional soft-tissue extension or edema (see Image 4).
• Computed tomography (CT) scanning may be helpful in defining the extent of the lesion within the bone, especially if the bone is in a more anatomically complex area, such as the hand, foot, or spine.
• Benign pulmonary metastases occasionally may occur with chondroblastoma; therefore, a chest radiograph should be obtained. A CT scan of the chest may be used to further evaluate any suspicious areas. These pulmonary lesions are resectable and curable.

Procedures

• If malignancy is not suspected based on clinical and radiographic features, tissue may be obtained for diagnosis at the time of surgical treatment of the lesion, and no preceding biopsy is needed. However, histologic confirmation by frozen section should be sought before proceeding with definitive treatment. If the lesion appears atypical on appropriate imaging studies, a needle or incisional biopsy should be performed before definitive treatment is undertaken.

Histologic Findings

Chondroblastomas are lobulated tumors that consist of grayish-pink soft tissue intermixed with bluish chondroid tissue and calcifications. The lesions may have many hemorrhagic cystic areas.

The tumors are composed of sheets of neoplastic mononuclear chondroblasts with eosinophilic cytoplasm and grooved nuclei (see Image 5). Interspersed among the mononuclear cells are osteoclastlike giant cells. The chondroid matrix typically is pink; on rare occasions, the basophilic matrix seen in hyaline cartilage is present. Some chondroblastomas may have a spindle-cell component, which represents either spindle-shaped mononuclear cells or reparative cells of fibroblastic origin. One of the most characteristic findings in the histologic examination of chondroblastomas is linear deposition of calcification surrounding individual chondroblasts, creating a chicken-wire pattern (see Image 6). Calcification may be so extensive that the chondrocytes in the area are not viable. In sections with well-preserved chondroblasts, mitoses may be seen, but atypical mitoses are not present in benign chondroblastoma.

Cystic changes within chondroblastomas are common. Some represent secondary aneurysmal bone cysts, which are found in 20-25% of all patients with chondroblastomas. Other cysts are filled with serous fluid and are divided into unilocular or multilocular spaces. When these other cysts are present, the tumors are termed cystic chondroblastomas. Initially, there was concern that cystic chondroblastomas had a much higher recurrence rate than typical chondroblastomas, but later reports did not confirm this theory. Less frequently seen histologic findings are cellular atypia with enlargement and irregularity of chondroblast nuclei (occurring in 30% of cases); hemosiderin (in 25% of cases); surrounding cortical and soft-tissue permeation (in 5% of cases); myxoid areas (in 2% of cases); and vascular invasion (in 1% of cases).

Immunostaining occasionally can be helpful in confirming the diagnosis of chondroblastoma. S-100 protein is strongly positive in the mononuclear cells, although it is absent in multinucleated giant cells and is present only focally in tumors with a large cystic component. Chondroblastomas are also positive for vimentin. Reticulin stain reveals a honeycomb pattern.

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